1. Field of the Invention
This invention concerns disposable diapers, incontinent briefs, and the like.
2. Background Art
Disposable diapers are garments designed to be worn, primarily by infants, about the lower portion of the trunk and to receive discharged urine, feces, and other body fluids. Disposable diapers function to contain the discharged materials and isolate them both from the body of the wearer and from the wearer's surroundings.
For many years diapers were formed from pieces of cloth which were pinned about the lower portion of the wearer's trunk and which were intended to be laundered and reused. In more recent times, disposable diapers have come into vogue thereby freeing mothers (and others charged with the care of infants) from the distasteful task of collecting and laundering soiled cloth diapers. In addition to the logistical benefit provided by disposable diapers, modern embodiments frequently perform in a manner superior to that of cloth diapers in that they tend to present a dryer surface to the body of the wearer and tend to prevent soiling of the wearer's outer garments and other surrounding surfaces more effectively and efficiently than cloth diapers even when the latter are encased within rubber or plastic pants.
Disposable diapers, incontinent briefs, and the like normally comprise three elements: a liquid permeable topsheet intended to be placed next to the wearer's skin, a liquid impermeable backsheet which forms, in use, the outer surface of the diaper, incontinent pad, or the like; and an absorbent element interposed between the topsheet and the backsheet.
The topsheet is frequently a hydrophobic nonwoven fabric. It is readily fluid permeable so that urine will freely pass through it into the absorbent element. Its hydrophobic nature tends to cause its upper surface (i.e., the surface away from the absorbent core and, in use, adjacent the wearer's skin) to be dryer and, therefore, protected from the fluids absorbed within the absorbent element.
The absorbent element is, as its name implies, designed to receive and retain fluids which pass through the topsheet. It normally comprises layers of creped wadding or, more commonly, a batt of airlaid wood pulp fibers.
The backsheet functions to contain fluids within the absorbent element and to protect the wearer's outer garments and other surfaces from soiling by those fluids. Commonly, the backsheet comprises a fluid impermeable, vapor impermeable material such as polyethylene film.
While backsheets comprising impermeable materials do function to contain fluids within the absorbent core and to protect the wearer's outer garments from soiling, they are sometimes perceived as causing the diaper to be hot and uncomfortable. Further, their impermeability precludes the self-drying of the diaper which would otherwise occur because of evaporation of the fluids contained therein.
Backsheets which are impermeable to liquid but permeable to vapor are known as breathable backsheets and have been described in the art. Breathable backsheets provide a cooler garment and permit some self-drying of the diaper while it is being worn. As indicated, these breathable backsheets are intended to allow the passage of vapor through them while retarding the passage of liquid. For example, U.S. Pat. No. 3,156,242, issued to Crowe, Jr. on Nov. 10, 1964, teaches the use of a microporous film as a breathable backsheet. U.S. Pat. No. 3,881,489, issued to Hartwell on May 6, 1975, teaches a breathable backsheet comprising, in combination, two layers: a low-void volume perforated thermoplastic film and a porous high-void volume hydrophobic tissue. U.S. Pat. No. 3,989,867, issued to Sisson on Nov. 2, 1976, teaches a breathable backsheet provided with tapered hollowed bosses which prevent the passage of liquids while allowing vapors to pass readily therethrough. (These three patents are incorporated herein by reference.)
As a general matter, the last two cited patents, provide for breathability across substantially the entire outer surface of the diaper. U.S. Pat. No. 4,341,216, issued to Obenour on July 27, 1982, incorporated herein by reference, describes and claims a somewhat different exemplary breathable backsheet. One practical effect of this invention is to tend to restrict the vapor permeability of the breathable backsheet in the crotch region relative to the vapor permeability of the backsheet in the waist regions.
While breathable backsheets do provide an improvement over the more common impermeable backsheets, and while those described in the last three mentioned patents are of particular value, developments providing for more comfortable and more serviceable diapers have still been sought.